September 20, 2012

An international team´s sequencing of the Pacific oyster´s genome has produced pearls of wisdom regarding the structure and adaptability of the tasty mollusk.

"The accomplishment is a major breakthrough in the international Conchological research, with great advancement in the fields of conchology and marine biology." said team member Fusui Zhang of the Chinese Academy of Sciences. "The study will provide valuable resources for studying the biology and genetic improvement of mollusks and other marine species. "

According to their report in the journal Nature, the researchers´ analysis of the genetic code provided more details on how Pacific oysters build their shells and cope with a potentially hostile environment.

Previous theories on oyster shell construction were not heavy on details, but the new study identified 259 shell proteins and revealed the complexity of the formation process. Some proteins such as Laminin and different collagens were highly expressed in shells, suggesting some relation to animal connective tissues.

As oysters are not only soft-bodied, but also sedentary, a hard exterior would not be sufficient protection if the environment around it were to rapidly change. Extreme shifts in temperature, large amounts of toxic detritus, or prolonged exposure to open air are all potential threats to a mollusk that inhabits tidal zones.

To identify the genetic mechanism responsible for the oyster´s temperature durability, the researchers located 88 different genes that code for heat shock protein 70, which guards sensitive tissue against extreme temperatures. By comparison, humans 17 genes that are responsible for the production of this protein and sea urchins, the oysters´ tidal zones companions, have just 39. Scientists said this amount of genes might explain why sun-baked oysters can tolerate temperatures up to 120 degrees Fahrenheit.

Oyster´s toxic tolerance and filtration is so well-known, New York City officials have proposed putting them in waterways around Manhattan to filter undesirables out of the harbor. The genetics team found that the oysters cope with potential pathogens through the intensive immune system in their gut. According to the report, the amount and types of genes dedicated to protecting the oyster´s digestive gland indicate that “the digestive system of this filter feeder is an important first-line defense organ against pathogens.”

The research team was also looking into the sea creature´s ability to survive in the open air during low tide and finding out why the oysters could survive prolonged exposure to air provided a window into just how adaptable these mollusks are. The researchers noted that over 4,400 different genes altered their expression when the animal was exposed to air. They also found a large number of duplicate genes, or paralogs, which suggested genetic repetition could be the key to the animal´s adaptability.

One result of the study could have a greater meaning for other, more complex animals–including humans. The analysis showed that Pacific oysters have 48 genes that code for proteins which inhibit ℠programmed cell death´. By comparison, the human genome has only eight.

Known as apoptosis, the study of this programmed cell death is a burgeoning topic in biology circles and many believe it plays a role in aging and cancer.

The Pacific oyster is the first-ever mollusk to have its genome sequenced and this study could pave the way for the sequencing of other equally edible mollusks, such as snails, scallops and octopuses.